A large frame heavy duty industrial gas turbine (IGT) engine is typically used to drive an electric generator and produce electrical energy. These engines can produce over 200 MW of electric power. An IGT engine will have a compressor with multiple rows or stages of rotor blades and stator vanes, a combustor with multiple can combustors arranged in an annular array (also referred to as a can annular combustor), and a turbine with multiple rows of rotor blades and stator vanes. An aero engine typically has an annular combustor instead of multiple can combustors arranged in an annular array as in the IGT engines.
The single largest hurdle to introducing new technologies into large frame power generation gas turbine engines is the risk that the new technology may fail during operation of the engine and result in tens of millions of dollars in equipment damage and possibly the cost of replacement electricity during the down time of the power plant. Thus, an owner of one of these engines is very reluctant to allow for the use of the engine in testing a new technology. As a result, it is very difficult to introduce new technologies into a utility power generation plant. Therefore most power generation manufacturers have test facilities to test as much as possible the components prior to going into production. Unfortunately the cost of test facilities and running the tests prohibits extensive testing and usually only allows for infant mortality issues to be discovered prior to installation of a new gas turbine engine at the utility site.
Testing a large IGT engine as a whole or testing a part or component of the engine is both very expensive and very difficult and complex. When a large engine is tested, the power generated must be dissipated. One method of dissipating the energy produced is to drive an electric generator and dump the electrical power produced. The excess electrical power produced during testing can be supplied back into the electrical grid. However, this can become a real problem with the electric power company. Since the engine testing might only last for a few hours, supplying this large amount of electricity to the grid for a few hours and then stopping causes real problems with the power company, especially if the power suddenly stops due to a problem during the test which trips the gas turbine engine offline.
Another problem with testing aero engines or large frame engines is that the cost to test is very high. In some IGT engine test beds, instead of using an electric generator to supply the resistance load, a water break or electrical heater resistors can be used to dissipate the load produced by the engine. These methods of dissipating the load have advantages over the electrical power production described above in that the disturbance to the electrical grid is not produced. However, the disadvantage is that all of the energy produced is lost.
In a power plant that uses an IGT engine to drive a generator and produce electrical power, the electrical power required by the local community cycles from high loads (peak loads) to low loads such as during cool days or at night. One process to match electric supply with demand of an electrical power plant is to make use of compressed air energy storage (CAES) system. At low loads, instead of shutting down an engine, the engine is used to drive a compressor instead of an electric generator to produce high pressure air that is then stored within an underground cavern such as a salt mine cavern. A large amount of compressed air is collected and then used to supply the engine during the peak loads.
When testing a gas turbine engine such as a large industrial engine or an aero engine or a component (such as a combustor) of one of these engines, the engine or component needs to be tested at different operating condition other than just the steady state condition. Engine partial load conditions must be tested for and therefore requires different fuel and compressed air flows. Also, the loads on the engine vary during the testing process from a full load at the steady state condition to partial loads. Thus, the amount of energy dissipated varies during the engine testing process.
Testing of a component of a large frame heavy duty industrial gas turbine engine is also required. Each of the components of an engine requires testing. The compressor, the combustor or the turbine can be tested as a separate unit from the engine. For example, in the testing of a combustor, a large volume of compressed air at high pressure (15-100 bars) is required to be supplied to the combustor to be burned with a fuel for testing. One or more compressors are required to produce this large volume of compressed air in order to recreate the actual pressure and flow produced by the compressor of the gas turbine engine that is delivered to the combustor to produce the hot gas stream passed through the turbine. Thus, a large electric motor with a power output of 20-200 MW and over is required to drive the compressor or compressors. Thus, testing of combustors requires a large capital expense and maintenance requirements.
When a component of a large industrial or aero gas turbine engine is to be tested, such as a combustor module or a turbine module or a compressor module, the entire engine is operated just to test that one component module. The entire engine is required to be operated in order to produce the conditions required to test that component module. Thus, it is very costly to test a single component module in a gas turbine engine when the entire engine is to be operated. Also, during operation of the gas turbine engine for testing one of the component modules such as a turbine module, a load is connected to the turbine in order to create a resistance during the testing process. As described above in the entire engine testing process, this load is typically lost or difficult to dissipate.
In testing of a compressor module, the compressed air produced during the testing process is wasted due to the high cost of storing the compressed air for future use. Thus, the energy produced in the testing process of a compressor module is also wasted.
An airfoil that requires a high Mach number of air flow for testing is typically supplied with compressed air from a compressed air storage tank that is relatively small and very heavy in construction to withstand the high pressures. Because of the limited size of the compressed air tank, the testing period is on the order of a few seconds which limits the accuracy of the test data and the types of data that can be measured.
Recently, several gas turbine Original Equipment Manufacturers (OEM's) have indicated a need for combustion research capability that far exceeds the flow capacity and pressure rations of existing facilities. This requirement for new combustion research facilities is motivated in the first instance by the need to design more environmentally benign gas turbines producing much reduced greenhouse gas emissions using hydrogen or, in the interim, blended hydrogen fuels. This requirement coincides with the rust-out of existing OEM combustion research facilities and the need to relocate existing facilities away from urban areas.
There is a pressing market requirement for a combustion research facility having significantly increased air mass flow rate and compression ratios than currently exist. The combustion research capacity and capability sought is necessary for next generation industrial gas turbines that will employ much higher pressure ratios than today's engines and will burn a variety of gaseous and liquid fuels with ever reducing green house gas emissions. Hydrogen produced from environmentally benign coal gasification is a key green target for the US government, based on extensive USA coal reserves and energy security agenda.
The National Research Council Institute for Aerospace Research (IAR) Gas Turbine Laboratory (GTL) already performs similar combustion research and technology demonstration. GTL R&TD is on both conventional and alternative fuels but at lower pressure ratios and air mass flow rates than are required for future technology development, demonstration and validation. The minimum facility air mass flow rate and operating pressure ratio that would be sufficient for this facility would be 150 lb/sec at a pressure ratio of 60:1. This requires a compressor drive power of 80 MW although redundancy would be a highly desirable facility attribute. The Compressor Institute design standard dictate that no more than 40 MW of compressor capacity be driven by one shaft. This means that at least two 40 MW gas turbines would be required, however, it may be prudent to use more than two drive gas turbines to enable cost effective delivery of less than one engine size class. This size test facility is estimated to cost around 200 Million. A more desirable facility capacity would provide 300-550 lb/sec of air at a minimum pressure ratio of 60:1, but would require a compressor drive capacity of around 150 MW. A full capacity facility would deliver 550 lb/sec of air at the 60:1 pressure ratio, but with a capital investment in excess of 600 Million.
Transient blow down testing is a technique that has been used for many years in aerospace testing. This technique is used to reduce the size and cost of compression and vacuum pumps required to develop the conditions required for a test. For example, a compressor can be run for days or longer to fill a tank to very high pressure and or a vacuum chamber to very low pressure. The gas is then released for testing. Depending on the mass-flow required during the test, the actual test time can vary from milliseconds up to many minutes. While the cost of the compression and vacuum equipment is kept low using the blow down facility idea, the cost of the pressure and vacuum tanks become very large. NASA Langley has some of the largest high pressure tanks available for testing to create very high Mach number flows.